Portable electronic devices such as laptop computers, LCD digital photo frames, mobile phones, and mp3 players require power to operate. Often, these devices use rechargeable batteries to provide power. The batteries are typically recharged by plugging a charger into the portable device or by removing the battery from the portable device and separately recharging the battery using a wired charger.
The cables that once restricted electronic devices are gradually being rendered unnecessary by wireless communication technology, and as the circuits that constitute the electronic devices shrink, only the power cords and batteries continue to restrict the portability of mobile electronic devices.
Current trends are leading towards going completely wireless. This means that portable devices can remain portable and can avoid having to ‘plug-in’ for power charging. Electro-magnetic inductive charging uses a coil to create an electromagnetic field across a charging station surface. The device then converts power from the electromagnetic field back into usable electricity, which is put to work charging the battery. Two coils are brought close to each other and when current is passed through one, the generated magnetic flux causes electromotive force to be generated in the other.
In order to reduce unnecessary generation of magnetic flux, for example when no receiver is positioned to receive the magnetic flux or when the battery associated with the receiver is already charged, techniques to determine whether a valid load is placed in position with respect to the transmitting coil and to determine the charging status of the load have been developed. In order to determine if a valid load is placed on the transmitting coil and to determine the charging status, a communication link is often used between the transmitting unit and the receiving unit. Such a link is often also used to determine whether multiple loads are placed on the transmitter. However, a communication link adds cost and size to the system, which is not desirable for a compact receiving unit to be integrated inside a portable device. Alternatively, a communication system, such as a complex DSP system, can be used to extract system operating parameters from the transmitter to determine the operating status of the system. However, such systems are typically complicated and consume large amounts of power which reduce system efficiency and increase system cost.
Accordingly, there still exists a need in the art for an efficient method and apparatus to determine whether a valid load is positioned to be charged and the charging status of the load.